2025/10/20 by Casey Y. Lam, Lam, Casey Y., Joshua D. Simon +9
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2510.17746
openalex publication_date 2025/10/20 · openalex created_date 2025/10/22 · openalex updated_date 2026/07/28
Stellar-mass black holes (BHs) above 30 M_\odot are predicted to form from low-metallicity progenitors, but direct detections of such systems in the Milky Way remain scarce. Motivated by the recent discovery of Gaia BH3, a 33 M_\odot BH with a very metal-poor giant companion, we conduct a systematic search for additional systems. Approximately 900 candidates are identified with Gaia as having significant deviations from single-star astrometric motion, evidence of RV variability, and low metallicities inferred from Gaia XP spectra. We obtain single epoch high-resolution spectra for over 600 of these sources with Magellan/MIKE and Lick/APF and measure independent RVs with ≈ 1 km s-1 precision. After removing contaminants such as hot stars, pulsators, eclipsing binaries, and hierarchical triples, we identify about 15 promising candidates with large RV amplitudes or offsets from the Gaia reported values. This program establishes a well-characterized sample of BH candidates for detailed orbital modeling once Gaia DR4 epoch astrometry and RVs are released in late 2026; multi-epoch RV follow-up is ongoing. Together, the Gaia and ground-based data will place new constraints on the demographics of BHs with metal-poor companions and test theoretical predictions linking low metallicity to the formation of the most massive stellar remnants.